Could this be a Normal Map?
In your example, the big extruding portion is geometry.

In the general case, it very much depends on how close you look at it and at what angle.

With a normal map you always see all faces of a detail. From some angles it can seem wrong since they are facing away from you.

Here we have some geometry represented by... geometry and a normal map. Normal map below. Can you tell wich one is the normal map? Yes, of course you can. But this is realy up close. Still, if you are rendering a space ship and are flying by it's side, go for geometry.